Let's talk Tweeters!


Another thread which talked about specific speaker brands was taken over, so I’d like to start a new one.

Mind you, I do not believe in a "best" type of tweeter, nor do I believe in a best brand of speaker, so lets keep that type of conversation out, and use this instead to focus on learning about choices speaker designers make and what that may mean to the end user.

There is no such thing as a speaker driver without trade offs. Some choices must be forsworn in exchange for another.

In the end, the materials used, magnet and motor structure, and crossover choices as well as the listening room come together to make a great speaker, of which there are many. In addition, we all listen for different things. Imaging, sweetness, warmth, detail, dance-ability and even efficiency so there is no single way to measure a driver and rate it against all others.

Also, please keep ads for your 4th dimensional sound or whatever off this thread. Thanks.
erik_squires
Hi   @erik_squires    over the years, at Marcof we heavily modified the old Motorola Piezo's... In the end, a tweeter with the reputation of being harsh and brittle ended up being pretty good.  They are amazingly fast, they remind me of a dryer version of a ribbon after mods... The best current single current model available now is the CTS KSN-1141.....If you ever end up wanting to try them, private message me and I'll send you mods for them.  Tim


sorry I didn't say... to your question,  yes, it is because their inherent capacitance, without a crossover, they come in on their own at 1800 hz. 
Thanks Tim!! I'm done with speaker building for a while. I made the speakers they'll bury me with, though I still keep tweaking the crossovers. :)

Best,

E
...arriving late, as usual...

Hey, bgpowell...I've heard of and been to the Newform site.  Been curious about their drivers, how do they sound to you vs. any other line source ribbon/planar of that design that you may have run into?  Most of that type ( Bohlender-Graebner 's, and the like) tend to be dipoles instead of monopoles.  Being a dipole/omni fan in general, I'm curious and would like to hear a critique'...*S*

Erik wrote: Let's focus on learning about choices speaker designers make and what that may mean to the end user.

Duke replies: I can't speak for any other designers, but for me speaker design starts with figuring out what the priorities are, and then hopefully finding a way to accomplish them (or come as close as is practical) within whatever constraints are imposed. So the system concept comes first, and then the design specifics follow. Thus I see tweeters (and every other part of a speaker) as just part of a system, and no more than a means to an end, which in high-end home audio is usually something like “a sufficiently convincing perception of listening to live music”.

Erik: First, for any given type of dispersion, speakers need to roll off more or less evenly. You don’t want to be 15 degrees off axis and only hear the mid-range. Ideally the speaker’s dispersion is even across as much of the response as possible, but usually this can only be done starting in the upper bass.

Duke: Yes! The radiation pattern plays a far greater role in what we perceive than most people appreciate. Most of the sound we hear in most home audio systems starts out being dispersed off-axis.

Erik: Next, the wider the dispersion, the more early reflections you may encounter, which can severely affect the frequency response and imaging.

Duke: Agreed. In general early reflections are detrimental, but later reflections can be quite beneficial.

Erik: The very large diaphragms of ESL speakers (Martin Logan/InnerSound, etc.) have fabulous clarity thanks to this effect. They can sound like you have headphones on even with very little room treatment.

Duke: Dipolar electrostats typically have a narrow radiation pattern that minimizes early reflections, and then have a spectrally-correct backwave that reflects off the wall behind the speakers. If the panels are far enough out into the room, that backwave energy is sufficiently late-arriving to be quite beneficial.

Erik: Drivers with different dispersion patterns _may_ also have different rate of decay. Consider a hybrid ESL + cone woofer. The woofer radiates omni-directionally and the wavefront looses energy the fastest, while the ESL panel is a plane wave, with narrow dispersion and looses energy more slowly.

Duke: This would be an example of an extreme radiation pattern discrepancy (narrow-pattern line-source panel combined with quasi-omni point-source woofer). Unfortunately it is not possible to equalize such a system so that the first-arrival sound and the reverberant sound have the same spectral balance (something that would be psychoacoustically desirable – I can explain why if anyone is interested). The best we can hope for is a juggling of tradeoffs that works at our chosen listening distance. In general, the lower the crossover frequency between woofer and panel, the better, as long as we don't overly compromise something else. 

Erik: Two of the most important measurements for me are Cumulative Spectral Decay and compression. The first measures energy storage, or "blur" that a tweeter adds to the sound because it won’t stop fast enough. The second measures how a tweeter’s response changes at different volumes.

Duke: We want to minimize anything that's a source of audible coloration, and in the tweeter region, what's happening in the time domain matters a great deal.

You mentioned compression – great job of paying attention to something that matters, but doesn't show up on a spec sheet! Thermal compression effects not only suck the dynamic life out of the sound, they are often responsible for a speaker system's tonal balance changing with volume level, which can happen if the various drivers have differing thermal compression characteristics (which they usually do).

Erik: Usually when I hear about issues integrating woofers with very light tweeters it's a frequency response issue, and integration with the room issue.

Duke: Note that the “frequency response” we hear is NOT the one in the published curve – that is only the on-axis response, which may not even be our first-arrival sound if we're sitting off-axis. And then the reverberant energy – remember that's usually most of the sound that reaches our ears - may well (and usually does) have a significantly different spectral balance. At the risk of over-simplifying, the “frequency response” that we perceive is a weighted average of the two. So what comes across as a room integration issue may well have its roots in a radiation pattern discontinuity in the crossover region. Thus the room gets blamed for colorations that can be traced back to problems in the radiation pattern, which in turn are (arguably) loudspeaker design deficiencies.

A few additional thoughts:

Imo one incorrect approach to speaker design would be this: Take “the best woofer”and “the best midrange” and “the best tweeter” and combine them using “the best crossover” and put them into “the best enclosure”. This can easily result in an overly expensive speaker whose different parts do not play well together, resulting in a lack of coherence that becomes distracting over time. This would be an example of putting the design specifics first.

Imo one correct approach to speaker design would be this: Choose all of the components based on how well they will work together with each other, with the room, and even with the amplifier towards achieving an intelligently-selected perceptual goal. This would be an example of putting the system concept first.

So my opinion on tweeters is, they are just one part of a system, and imo it's not cost-effective to trade off good system synergy for the sake of using “the best tweeter”. To give an example, I don't think anyone has accused Andrew Jones of using the best tweeters, but those of us who compete with him must admit that he is a master of system synergy.

Given my particular, perhaps somewhat unorthodox set of priorities, tweeters whose radiation patterns change significantly with frequency are not the ideal tools for what I'm trying to do, though they can be made to work reasonably well with careful juggling of tradeoffs. My preference is generally for tweeters that use a particular type of waveguide or horn: Constant-directivity with low diffraction, with the intention of crossing over where the woofer's radiation pattern approximately matches the horn's. System concept first, design specifics second.